1. Field of the Invention
The present invention generally relates to lighting fixtures and signs, and more particularly to an improved exit sign having a multiplicity of miniature incandescent light bulbs.
2. Description of the Prior Art
Every state in America has certain regulations concerning the proper placement of exit signs. Such signs are used to insure safe and efficient evacuation of a building in case of an emergency, such as fire. For example, Texas Revised Civil Statutes Annotated article 3965 requires, inter alia, "at least one red light at each exit to each fire escape, and one guide sign for every twenty-five lineal feet of hallway or corridor leading to such fire escape."
Exit signs typically are box-shaped, with an outer metallic sheet having a cutout forming the word "EXIT." A translucent piece of red plastic lies adjacent to the outer sheet, and an incandescent light bulb inside the box illuminates the red plastic from behind. Arrows on the sign indicate the direction of the nearest fire escape. The light source is usually connected to an emergency power supply, or a battery backup. This satisfies the requirement of having both a guide sign and a red light, although sometimes a separate red light bulb is placed adjacent to a exit sign having external illumination only.
There are, however, several drawbacks to such prior art devices. First of all, if the light bulb within the sign (or the bulb providing external illumination) burns out, the device is practically useless. Although the word "EXIT" may still be discernable is good light, the purpose of the sign is to assist tenants under urgent conditions, such as a power black out, when no external light is available. Some exit sign manufacturers add a second light bulb to guard against such an occurrence, but there is still a chance that both bulbs will burn out. Furthermore, even if two bulbs are used, illumination of the sign is cut in half which may be critical when visibility is poor, e.g., in a smokey hallway.
The problem of smoke relates to another disadvantage of prior art exit signs. Even if all of the bulbs within the sign are working properly, output wattage of the bulb (typically measured in lamberts) is diminished by the transmission of the light through the translucent piece of red plastic. In other words, it is much more difficult to discern the pattern of the letters when using backlighting (or, for that matter, reflective illumination), as compared to direct viewing of the light bulb filament. Concentrated, bright light is necessary to penetrate the dense carbon particles suspended in the smoke.
A third limitation of prior art devices concerns the angle of viewing. According to Lambert's law, the luminous intensity in a given direction radiated or reflected by an illuminated surface varies as the cosine of the angle between that direction and the normal to the surface. In simpler terms, as one views the exit sign from more of a side angle, the intensity of the light decreases. Thus, there is a chance that persons looking in the direction of the sign, but at a side angle, will not perceive the sign to be an exit guide at all. It would, therefore, be desirable and advantageous to devise as exit sign overcoming the above limitations by providing a multiplicity of light bulbs arranged in a manner to yield increased brightness and an increased angle of viewing.